[GWP-ASan] Move random-related code in the allocator
We need to have all thread specific data packed into a single `uintptr_t`
for the upcoming Fuchsia support. We can move the `RandomState` into the
`ThreadLocalPackedVariables`, reducing the size of `NextSampleCounter`
to 31 bits (or we could reduce `RandomState` to 31 bits).
We move `getRandomUnsigned32` into the platform agnostic part of the
class, and `initPRNG` in the platform specific part.
`ScopedBoolean` is replaced by actual assignments since non-const
references to bitfields are prohibited.
`random.{h,cpp}` are removed.
Differential Revision: https://reviews.llvm.org/D89908
GitOrigin-RevId: 9903b0586cfb76ef2401c342501e61e1bd3daa0f
diff --git a/guarded_pool_allocator.cpp b/guarded_pool_allocator.cpp
index b2602e4..93fe5c2 100644
--- a/guarded_pool_allocator.cpp
+++ b/guarded_pool_allocator.cpp
@@ -10,7 +10,6 @@
#include "gwp_asan/optional/segv_handler.h"
#include "gwp_asan/options.h"
-#include "gwp_asan/random.h"
#include "gwp_asan/utilities.h"
// RHEL creates the PRIu64 format macro (for printing uint64_t's) only when this
@@ -38,15 +37,6 @@
// referenced by users outside this translation unit, in order to avoid
// init-order-fiasco.
GuardedPoolAllocator *SingletonPtr = nullptr;
-
-class ScopedBoolean {
-public:
- ScopedBoolean(bool &B) : Bool(B) { Bool = true; }
- ~ScopedBoolean() { Bool = false; }
-
-private:
- bool &Bool;
-};
} // anonymous namespace
// Gets the singleton implementation of this class. Thread-compatible until
@@ -64,7 +54,7 @@
return;
Check(Opts.SampleRate >= 0, "GWP-ASan Error: SampleRate is < 0.");
- Check(Opts.SampleRate <= INT32_MAX, "GWP-ASan Error: SampleRate is > 2^31.");
+ Check(Opts.SampleRate < (1 << 30), "GWP-ASan Error: SampleRate is >= 2^30.");
Check(Opts.MaxSimultaneousAllocations >= 0,
"GWP-ASan Error: MaxSimultaneousAllocations is < 0.");
@@ -155,13 +145,15 @@
void *GuardedPoolAllocator::allocate(size_t Size) {
// GuardedPagePoolEnd == 0 when GWP-ASan is disabled. If we are disabled, fall
// back to the supporting allocator.
- if (State.GuardedPagePoolEnd == 0)
+ if (State.GuardedPagePoolEnd == 0) {
+ ThreadLocals.NextSampleCounter = AdjustedSampleRatePlusOne - 1;
return nullptr;
+ }
// Protect against recursivity.
if (ThreadLocals.RecursiveGuard)
return nullptr;
- ScopedBoolean SB(ThreadLocals.RecursiveGuard);
+ ScopedRecursiveGuard SRG;
if (Size == 0 || Size > State.maximumAllocationSize())
return nullptr;
@@ -241,7 +233,7 @@
// Ensure that the unwinder is not called if the recursive flag is set,
// otherwise non-reentrant unwinders may deadlock.
if (!ThreadLocals.RecursiveGuard) {
- ScopedBoolean B(ThreadLocals.RecursiveGuard);
+ ScopedRecursiveGuard SRG;
Meta->DeallocationTrace.RecordBacktrace(Backtrace);
}
}
@@ -286,6 +278,15 @@
FreeSlots[FreeSlotsLength++] = SlotIndex;
}
+uint32_t GuardedPoolAllocator::getRandomUnsigned32() {
+ uint32_t RandomState = ThreadLocals.RandomState;
+ RandomState ^= RandomState << 13;
+ RandomState ^= RandomState >> 17;
+ RandomState ^= RandomState << 5;
+ ThreadLocals.RandomState = RandomState;
+ return RandomState;
+}
+
GWP_ASAN_TLS_INITIAL_EXEC
GuardedPoolAllocator::ThreadLocalPackedVariables
GuardedPoolAllocator::ThreadLocals;
diff --git a/guarded_pool_allocator.h b/guarded_pool_allocator.h
index 12049e1..cf31437 100644
--- a/guarded_pool_allocator.h
+++ b/guarded_pool_allocator.h
@@ -13,7 +13,6 @@
#include "gwp_asan/definitions.h"
#include "gwp_asan/mutex.h"
#include "gwp_asan/options.h"
-#include "gwp_asan/random.h"
#include "gwp_asan/stack_trace_compressor.h"
#include <stddef.h>
@@ -195,17 +194,40 @@
// the same cache line for performance reasons. These are the most touched
// variables in GWP-ASan.
struct alignas(8) ThreadLocalPackedVariables {
- constexpr ThreadLocalPackedVariables() {}
+ constexpr ThreadLocalPackedVariables()
+ : RandomState(0xff82eb50), NextSampleCounter(0), RecursiveGuard(false) {
+ }
+ // Initialised to a magic constant so that an uninitialised GWP-ASan won't
+ // regenerate its sample counter for as long as possible. The xorshift32()
+ // algorithm used below results in getRandomUnsigned32(0xff82eb50) ==
+ // 0xfffffea4.
+ uint32_t RandomState;
// Thread-local decrementing counter that indicates that a given allocation
// should be sampled when it reaches zero.
- uint32_t NextSampleCounter = 0;
+ uint32_t NextSampleCounter : 31;
// Guard against recursivity. Unwinders often contain complex behaviour that
// may not be safe for the allocator (i.e. the unwinder calls dlopen(),
// which calls malloc()). When recursive behaviour is detected, we will
// automatically fall back to the supporting allocator to supply the
// allocation.
- bool RecursiveGuard = false;
+ bool RecursiveGuard : 1;
};
+ static_assert(sizeof(ThreadLocalPackedVariables) == sizeof(uint64_t),
+ "thread local data does not fit in a uint64_t");
+
+ class ScopedRecursiveGuard {
+ public:
+ ScopedRecursiveGuard() { ThreadLocals.RecursiveGuard = true; }
+ ~ScopedRecursiveGuard() { ThreadLocals.RecursiveGuard = false; }
+ };
+
+ // Initialise the PRNG, platform-specific.
+ void initPRNG();
+
+ // xorshift (32-bit output), extremely fast PRNG that uses arithmetic
+ // operations only. Seeded using platform-specific mechanisms by initPRNG().
+ uint32_t getRandomUnsigned32();
+
static GWP_ASAN_TLS_INITIAL_EXEC ThreadLocalPackedVariables ThreadLocals;
};
} // namespace gwp_asan
diff --git a/options.inc b/options.inc
index 6cdddfb..c81e1f4 100644
--- a/options.inc
+++ b/options.inc
@@ -29,7 +29,7 @@
GWP_ASAN_OPTION(int, SampleRate, 5000,
"The probability (1 / SampleRate) that an allocation is "
"selected for GWP-ASan sampling. Default is 5000. Sample rates "
- "up to (2^31 - 1) are supported.")
+ "up to (2^30 - 1) are supported.")
// Developer note - This option is not actually processed by GWP-ASan itself. It
// is included here so that a user can specify whether they want signal handlers
diff --git a/platform_specific/guarded_pool_allocator_posix.cpp b/platform_specific/guarded_pool_allocator_posix.cpp
index a8767a4..c2cd244 100644
--- a/platform_specific/guarded_pool_allocator_posix.cpp
+++ b/platform_specific/guarded_pool_allocator_posix.cpp
@@ -16,6 +16,7 @@
#include <string.h>
#include <sys/mman.h>
#include <sys/types.h>
+#include <time.h>
#include <unistd.h>
#ifdef ANDROID
@@ -33,6 +34,11 @@
}
namespace gwp_asan {
+
+void GuardedPoolAllocator::initPRNG() {
+ ThreadLocals.RandomState = time(nullptr) + getThreadID();
+}
+
void *GuardedPoolAllocator::mapMemory(size_t Size, const char *Name) const {
void *Ptr =
mmap(nullptr, Size, PROT_NONE, MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
diff --git a/random.cpp b/random.cpp
deleted file mode 100644
index 927709a..0000000
--- a/random.cpp
+++ /dev/null
@@ -1,29 +0,0 @@
-//===-- random.cpp ----------------------------------------------*- C++ -*-===//
-//
-// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
-// See https://llvm.org/LICENSE.txt for license information.
-// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-//
-//===----------------------------------------------------------------------===//
-
-#include "gwp_asan/random.h"
-#include "gwp_asan/common.h"
-
-#include <time.h>
-
-// Initialised to a magic constant so that an uninitialised GWP-ASan won't
-// regenerate its sample counter for as long as possible. The xorshift32()
-// algorithm used below results in getRandomUnsigned32(0xff82eb50) ==
-// 0xfffffea4.
-GWP_ASAN_TLS_INITIAL_EXEC uint32_t RandomState = 0xff82eb50;
-
-namespace gwp_asan {
-void initPRNG() { RandomState = time(nullptr) + getThreadID(); }
-
-uint32_t getRandomUnsigned32() {
- RandomState ^= RandomState << 13;
- RandomState ^= RandomState >> 17;
- RandomState ^= RandomState << 5;
- return RandomState;
-}
-} // namespace gwp_asan
diff --git a/random.h b/random.h
deleted file mode 100644
index 953b989..0000000
--- a/random.h
+++ /dev/null
@@ -1,23 +0,0 @@
-//===-- random.h ------------------------------------------------*- C++ -*-===//
-//
-// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
-// See https://llvm.org/LICENSE.txt for license information.
-// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-//
-//===----------------------------------------------------------------------===//
-
-#ifndef GWP_ASAN_RANDOM_H_
-#define GWP_ASAN_RANDOM_H_
-
-#include <stdint.h>
-
-namespace gwp_asan {
-// Initialise the PRNG, using time and thread ID as the seed.
-void initPRNG();
-
-// xorshift (32-bit output), extremely fast PRNG that uses arithmetic operations
-// only. Seeded using walltime.
-uint32_t getRandomUnsigned32();
-} // namespace gwp_asan
-
-#endif // GWP_ASAN_RANDOM_H_
